Purification of aromatic hydrocarbons



Patented May 19, 1953 PURIFICATION OF AROMATIC HYDRO CARBONS Frank P. Hazlett, Pittsburgh, Pa., assignor to Jones & Laughlin Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Application page 11, 1952,

Serial No. 266107 6 Claims. (Cl; 260-674) This invention is concerned with the purification of aromatic hydrocarbons, and more particularly with the reduction of the parafiin content of such hydrocarbons. This application I is a continuation in part of my application Serial No. 57,839, filed June 16,1949, and now abandoned. 7 7

An object of my invention is the provision of an improved process of hydrocarbon purification using aluminum chloride. Another object is the improvement of the efiiciency of such processes by the use of promoters. Another object is to reduce the cost of such processes. Other objects will appear in the course of the disclosure of my invention.

The common aromatic hydrocarbons benzene, toluene, and xylene, which may be recovered as by-products in the coking of coal, find considerable use as raw materials in further chemical manufacture. For these purposes it is generally required that the content of unwanted constituents be quite low. One class of unwanted constituents is the paraffins, which some toluene specifications, for example, require to be held below 0.2% when the toluene is to be used in the carbons with this degree of purity without some auxiliary purifying treatment.

The term paraflins as here used is a trade expression referring to nonaromatic compounds which are unsulfonatable and have boiling points close to that of the aromatic hydrocarbon. For example, in benzene of commercial grade produced from coal-coking operations, these parafiins" have been found to be primarily naphthenic and to include the following compounds [see John R. Anderson and Carl J. Engelder, Industrial and Engineering Chemistry, vol. 3'7, pp. 541-3 (1945), and Chemical Abstracts, vol. 39. p. 3146/3 (1945)]:

(l) Cyclohexane;

(2) Methylcyclohexane;

(3) 3-methylhexane or 3 -ethylpentane or both;

(4) Heptane or 2,2,4 trimethylpentane or both;

(5) 1,1-dimethylcyclopentane; and

(6) Trans-1,2-dimethylcyclopentane or trans- 1,3-dimethylcyclopentane or both. i

A considerable number of methods for reducing the percentage of these "paraflins have been devised, including adsorption of the parafiins on sold adsorbents, solvent extraction, azeotropic distillation, extractive distillation, and chemical reaction, particularly treatment of the parafiins to produce less undesirable lower or higher boiling point compounds. Of these various methods the last has been found to reduce the parafiin content to lowest values.

The said treatment is generally carried out by reacting the parafiins with an acid-reacting metal halide, such as aluminum chloride. Under favorable conditions,'the paraffin content of a commercially refined hydrocarbon so treated can be reduced to the 0.2% limit imposed by a number of users, provided that the temperature is kept closely below the boiling point of the aromatic hydrocarbon. Repeated treatment may be necessary in some instances to reduce the paraiiin content to the maximum limit of 0.2%; for example, if the initial paraffin content happens to be high as a result of the particular operating conditions of the coke oven which produced the aromatic hydrocarbon. I have discovered, however, a process by which reaction of the parafiins in aromatic hydrocarbons can be carried out in one stage so completely that the unreacted parafiin content lies well below the lowest limits so far set by industrial users of toluene and other aromatic hydrocarbons.

My invention consists, essentially, in reacting the hydrocarbon with aluminum chloride to which is added, as promoter, alpha picoline. Olefins and any tar formed are afterwards removed by known means. A single treatment, by the process of my invention, of toluene, for example, containing upwards of 0.50% parafiins, not only produces purified toluene containing less than 0.10% of these compounds, but does so with full speed and effectiveness at relatively reduced temperatures such as C. and 50 C. This is well below the reaction temperature of close to C. necessary for maximum effectiveness when treating toluene with aluminum chloride alone.

The following examples illustrate the operation of my invention. In these examples a sample of paraflin containing toluene stock was obtained from a batch of toluene produced as a regular by-product of coal-coking operations and of commercially refined grade, sulphuric acid washed, which is not fully purified but meets the test for nitration grade toluene in A. S. T. M. Specification D841-47 as determined by the procedure described in A. S. T. M. Specification D851-47 (see vol. 5, A. S. T. M. Stand- 5. A method of reducing the percentage of para hydrocarbons in a. mixture of a small percentage of paraffin hydrocarbons dissolved as normally occurring impurities in a liquid aromatic hydrocarbon which is produced from coal and is from the group consisting of benzene, toluene and xylene, said paraffin hydrocarbons being unsulfonatable, non-aromatic and of such nature as to distill over with the aromatic hydrocarbon, comprising treating the said mixture with anhydrous aluminum chloride in amount between about 1% and 9% by weight of the aromatic hydrocarbon and alpha picoline in amount not less than 10% by weight of the aluminum as normally occurring impurities in liquid toluene produced from coal, said "paraflin hydrocarbons being unsulfonatable, nonaromatic and of such nature as to distill over with the toluene, comprising treating the said mixture at a temperature of about 50 C. to 80 C. at about atmospheric pressure with anhydrous aluminum chloride in amount about 3% by weight and alpha picoline in amount about 20% by weight of the anhydrous aluminum chloride, and agitating the mixture, until the content of "paraifin hydrocarbons is reduced to about 0.1% or less by volume in a single treatment.

FRANK P. HAZLETT.

Name Date Ipatiefi et a1. Aug. 3, 1937 Hepp et a1 Jan. 11, 1949 Number 

1. A METHOD OF REDUCING THE PERCENTAGE OF "PARAFFIN " HYDROCARBONS IN A MIXTURE OF A SMALL PERCENTAGE OF "PARAFFIN" HYDROCARBONS DISSOLVED AS NORMALLY OCCURING IMPURITIES IN A LIQUID AROMATIC HYDROCARBON PRODUCED FROM COAL, SAID "PARAFFIN" HYDROCARBONS BEING UNSULFONATABLE, NONAROMATIC AND OF SUCH NATURE AS A DISTILL OVER WITH THE AROMATIC HYDROCARBON, COMPRISING TREATING THE SAID MIXTURE WITH ANHYDROUS ALUMINUM CHLORIDE AND ALPHA PICOLINE, AT A TEMPERATURE AND PRESSURE BELOW THE BOILING POINT OF THE AROMATIC HYDROCARBON, UNTIL THE PERCENTAGE OF SAID "PARAFFIN" HYDROCARBONS IN THE MIXTURE IS REDUCED TO ABOUT 0.2% OR LESS BY VOLUME. 